1. Field of the Invention
This invention relates to an apparatus in which fine line patterns are etched or thin films are deposited on the surface of a semiconductor wafer by a plasma processing technique. More particularly, this invention relates to an apparatus for creating a plasma medium in a plasma processing reactor having three electrodes together with an optional magnetic enhancement.
2. Description of the Prior Art
Considerable interest exists in employing plasma processing techniques for patterning and/or depositing thin films on work pieces such as semiconductor wafers. The interest in plasma etching techniques stems from their generally better resolution and improved dimensional and shape control capabilities relative to standard wet chemical etching. Thus, plasma etching is being utilized increasingly in, for example, pattern delineation in the processing of semiconductor wafers to form very large scale integrated (VLSI) devices. The interest in plasma deposition techniques stems from their ability to deposit films of lower temperatures then conventional chemical vapor deposition techniques; to deposit more conformal films than conventional physical vapor deposition techniques; to deposit non-stoichoimetric films; and to simultaneously deposit and etch films resulting in a planarized deposition.
Various plasma dry etching processes that involve radio frequency generated plasmas are known. These processes include sputter etching which is described, for example, in J. Vac. Sci. Technol., Vol. 13 No. 5 pp. 1008-1022, September/October 1976, and reactive sputter etching which is described, for example, in Proc. 6 Int 1. Vacuum Congr. 1974, J. Appl. Phys., Suppl. to, Pt. 1, pp. 435-438, 1974. Also, U.S. Pat. No. 4,298,443 issued to Maydan discloses an apparatus for high throughput sputter etching or reactive sputter etching of a wafer comprising a multi-faceted wafer holder centrally disposed within a cylindrical chamber. A source of RF power is capacitively coupled to the wafer holder and the cylindrical chamber is grounded. By establishing a suitable plasma within the chamber simultaneous anisotropic etching of a plurality of wafers can be achieved in an apparatus of small size. In this teaching, only the central multi-faceted wafer holder is connected to a source of RF energy.
Enhanced etching of wafers can be achieved through the utilization of a mangetic field in combination with the electric field that is used to create the plasma. Articles such as V. Minkicwicz, Magnetic Field Control Of Reactive Plasma Etching, Applied Physics Letters, 35(5), 1979 and H. Okano, High Rate Reactive Ion Etching Using A Magnetron Discharge, ET Electrotech Seminar, Honolulu, Hawaii, Jan. 1, 1981 describe the use of magnetic fields in wafer etching devices. The Materials Research Corporation, Orangeburg, N.Y. has manufactured "Magnetron" Ion Etch Systems which utilize magnetic fields in plasma etch systems. U.S. Pat. No. 4,422,896 describes such a device.
Various plasma deposition processes that involve radio frequency generated plasmas are also known. Articles such as "Plasma Deposition of Inorganic Films", J. R. Hollahan and R. S. Rosler in Thin Film processes, Academic Press, New York 1978 p. 335.; W. Johnson, "Design of Plasma Deposition Reactors", Solid State Technology 25(4) 191 (1983); and M. Rand, J. Vac. Sci Tech. 16(2) 420 (1979). Also, U.S. Pat. No. 3,757,733 issued to Beinberg discloses an apparatus for the deposition of inorganic films on wafers comprising two parallel horizonal electrode disks within a cylindrical vacuum chamber. A source of RF power is capacitively coupled to the upper electrode, and the lower electrode is grounded. By establishing a a suitable plasma within the chamber, an inorganic film is deposited on wafers placed on the lower electrode. In this teaching only the upper electrode is connected to a source of RF energy. U.S. Pat. No. 4,223,048 issued to Engle discloses an apparatus for the deposition of inorganic films on wafers comprising two sets of interleaved planar electrodes disposed within an evacuable envelope and a means for establishing a plasma in the gaps defined between the interleaved electrodes. In this teaching only two electrical potentials are provided.